Hypodermic syringe having an adjustable plunger



S. AXELRAD HYPODERMIC SYRINGE HAVING AN ADJUSTABLE PLUNGER Filed Jan. 27, 1955 FIG. 4.

' INVENTOR SOL AXELRAD.

ATTORNEY United States Patent HYPODERMIC SYRINGE HAVING AN ADJUSTABLE PLUNGER Sol Axelrad, Woodmere, N. Y.; Corinne Axelrad, executrix of the estate of said Sol Axelrad, deceased, assiguor to Allergists Supply Co. Inc., New York, N. Y.

Application January 27, 1955, Serial No. 484,490

1 Claim. (Cl. 128-219) This invention relates to a hypodermic syringe having an adjustable plunger.

The principal object of this invention is the provision of a hypodermic syringe in which the plunger, and more particularly its packing, is diametrically adjustable so as to provide greater or lesser tolerance and pressure between it and the wall of the cylinder in which it is disposed.

It will be understood that excessive pressure between the plunger and cylinder wall will prevent proper functioning of the syringe since the plunger will not be readily movable within the cylinder and relative thereto. By the same token, insufficient pressure or excessive clearance between the plunger and the cylinder wall will prevent proper functioning of the syringe since there will be insufiicient suction on the suction stroke of the plunger and insufiicient pressure, and possibly some leakage, on the pressure stroke of the plunger.

In the present invention, the packing of the plunger is very quickly and readily adjusted to control the pressure which it will exert upon the inside of the cylinder wall. The adjustment is so quick that the plunger may be relatively free on its movement in forward direction to the forward or needle end of the cylinder and immediately prior to the rearward or suction stroke the plunger may be adjusted to increase its pressure upon the cylinder wall in order to provide adequate suction and thereafter adequate pressure on the pressure stroke and at the conclusion thereof the plunger may be adjusted to reduce its pressure upon the cylinder wall so that it may be withdrawn from the cylinder with great ease.

An important feature of this invention is the fact that the packing may be adjusted when it is situated at the forward end of the cylinder immediately adjacent the needle where it maybe adjusted to either increase or decrease its pressure upon the cylinder wall. The reason for this is the fact that the adjustment control is at the outer end of the plunger although the adjustment means proper is at its inner end. It will be understood that the plunger is provided at its outer end with a conventional knob by which it may be thrust inwardly for the pressure stroke or drawn outwardly for the suction stroke. It is this knob which serves as the adjustment control since it is by means of said knob that it is possible not only to move the plunger longitudinally of itself but also to turn it in either clockwise or counter-clockwise direction about its longitudinal axis.

The adjustment proper consists of a screw at the inner end of the plunger. It is on this screw that the packing is mounted. The screw itself is coaxial with the plunger with which it is in screw-threaded engagement. The head of the screw is knurled for engagement with the reduced or tapered forward end of the cylinder. Consequently, when the plunger is moved to its forwardmost position in the cylinder, the knurled head of the screw engages the reduced end of said cylinder and the plunger may be turned by means of its outer knob relative to the screw since the screw will be in frictional engagement with said reduced end of the cylinder. Depending upon the direc- 2,756,747 Patented July 31, 1956 ice tion of angular movement of the plunger, the head of the screw will either compress the packing against the inner end of the plunger and thereby cause it to swell out or the pressure of the head of the screw upon the packing will be diminished and the packing will thereby be enabled to contract to smaller transverse proportions.

The invention is illustrated in the accompaning drawing in which:

Fig. 1 is a side view of a hypodermic syringe made in accordance with this invention, the forward or needle end thereof being partly broken away to expose the forward end of the plunger.

Fig. 2 is a longitudinal section through said hypodermic syringe.

Fig. 3 is an enlarged, fragmentary sectional view of a portion of the lower end of said syringe, showing the engagement of the knurled screw at the forward end of the plunger withthe tapered annular shoulder which is situated at the forward end of the hollow cylindrical body of said syringe and between said cylindrical body and its needle receiving tip.

Fig. 4 shows the result of tightening the screw against the packing to cause said packing to press firmly against the side wall of the cylindrical body.

Fig. 5 is a transverse section on the line 55 of Fig. 2.

Fig. 6 is a transverse section on the line 6--6 of Fig. 2.

It will be seenin the drawing that the hypodermic syringe herein claimed has a cylinder 10 with an outwardly extending flange 12 at its upper or back end and a tubular tip 14 of relatively small diameter at its forward end. A tapered shoulder 16 is provided between the cylinder 10 proper and its tip 14. The cylinder may be calibrated in conventional manner and it may be made of glass or any other suitable material. in any conventional size.

The plunger 18 has a knob 20 at its outer end. This knob is either integral with the plunger or fixed thereto so that it will move integrally therewith. Knob 20 may be knurled to facilitate holding the same with the fingers and also turning it in either direction. At the inner or lower end of plunger 18 is a tapped hole 22 which is coaxial with said plunger and its knob 20. A screw 24 is inserted into said tapped hole 22 and it will be noted that said screw is provided with a knurled head 26 of approximately the same diameter as the plunger 18. Packing 28 is a cylindrical member which is mounted on screw 24 between the head of said screw and the lower or inner end of the plunger 18. The cylindrical packing member 28 is relatively long in the sense that its length approximates its diameter and it will be noted that it has flat parallel upper and lower ends. The lower end of plunger 18 is also fiat and it occupies a plane to which the longitudinal axis of said plunger is normal. Similarly, the knurled head 26 of the screw is also provided with flat parallel upper and lower faces to which the longitudinal axis of the screw is normal. The cylindrical packing is thereby situated with one flat end flat against the lower end of the plunger and its opposite flat end flat against the head of the screw.

It will be understood that the plunger and the screw may be made of any suitable material, such as stainless steel. The packing may also be made of any suitable material such as natural or synthetic rubber. It should be resilient and elastic, adapted to swell outwardly when squeezed in longitudinal direction and capable of contracting when released.

It will be understood from the foregoing, that when the plunger is thrust inwardly into the cylinder until the knurled head of the screw engages the tapered shoulder 16 of the cylinder, the plunger may be turned in either direction without turning the screw. The screw will thereby be caused to move axially relative to the plunger It may also be made and thereby to increase or decrease the distance from its head to the inner end of the plunger, depending upon the direction of angular movement of the plunger relative to the screw. In this way, the head of the screw may be caused to exert endwise pressure upon the packing by forcing it against the inner end of the plunger and the packing will thereby swell radially outwardly to apply greater pressure upon the cylinder wall. By the same token, the screw may be moved axially away from the plunger in order to decrease the endwise pressure of the head of the screw upon the packing and thereby to enable the packing to contract to smaller transverse proportions. The packing will thereby reduce its pressure upon the cylinder wall.

The foregoing is illustrative of a preferred form of this invention and it will be understood that this preferred form may be modified and other forms may be provided within the broad spirit of the invention and the broad scope of the claim.

I claim:

A hypodermic syringe, having a hollow cylindrical body, a tip for a needle at one end of said cylindrical body and an inwardly tapered annular shoulder between said cylindrical body and said tip, a plunger slidably mounted in said cylindrical body for longitudinal and angular movement therein, a knob connected to the upper end of said plunger for manually moving the plunger either longitudinally of itself and the cylindrical body or angularly about its longitudinal axis, the lower end of said plunger being flat and occupying a plane to which the longitudinal axis of the plunger is normal, a screw in screw-threaded engagement with said lower end of the plunger, coaxially therewith, said screw having a cylindrical head with flat faces at its upper and lower ends which occupy parallel 4 planes to which the longitudinal axis of the screw is normal, the cylindrical side of the screw head being knurled and frictionally engageable with the annular tapered shoulder between the cylindrical body and tip, and a cylindrical rubber packing mounted on said screw between the screw head and the lower end of the plunger, said cylindrical packing being approximately equal in length and diameter and having flat parallel ends to which its longitudinal axis is normal, one flat end of said packing bearing against the flat lower end of the plunger, the other flat end of the packing bearing against the adjacent flat face of the head of the screw, the diameter of said packing when in relaxed state being slightly smaller than the inside diameter of the cylindrical body to permit of movement of said packing relative to said cylindrical body, said packing being adapted to swell radially outwardly into frictional engagement with the inner wall of said cylindrical body when the screw is turned in one direction relative to the plunger to bring the screw head closer to the fiat lower end of said plunger and thereby to compress the packing, said packing being adapted to contract to its original condition when the screw is turned in the opposite direction to move the screw head away from the fiat lower end of the plunger, such movement of the screw relative to the plunger being effected by pressing the plunger inwardly in the cylindrical body to bring the screw head into frictional engagement with said tapered annular shoulder and then turning the knob at the upper end of said plunger in the desired angular direction.

References Cited in the file of this patent UNITED STATES PATENTS Re. 17,059 Hein Aug. 7, 1928 

